What is the output of this program?

#include<stdio.h>
#include<fcntl.h>
#include<sys/stat.h>
#include<sys/mman.h>
 
int main()
{
    int s_id;
    s_id = shm_open("shared_mem",O_CREAT|O_RDWR,0666);
    printf("%d\n",s_id);
    if(shm_unlink("shared_mem") == -1)
        perror("shm_unlink");
    return 0;
}

A. -1

B. 1

C. 2

D. 3

Answer: Option D